Spin waves, or magnons in quantum terms, arise when spins in magnets are disturbed and start rotating around their equilibrium positions. These rotations propagate through the magnetic material due to strong coupling between adjacent spins. Magnonics is an emerging research field that aims to encode information in both the amplitude and phase of magnons, and to use them to perform basic logical operations.
Magnonics at THz frequencies
To advance magnonics for future computing technology, spin waves need to be generated at nanoscale and THz frequencies (1 THz = 1 trillion hertz), enabling magnonic chips to operate up to 1000 times faster than current chips without energy loss from electric currents. Antiferromagnets, characterized by mutually antiparallel spin alignment, are widely regarded as the ideal medium to achieve this goal. However, driving magnons in antiferromagnets has long been notoriously difficult, and all protocols for implementing spin-wave logic have remained theoretical. "A few years ago, we overcame this obstacle by for the first time demonstrating that a short pulse of UV light can localize spin excitation within a few nanometers, allowing terahertz antiferromagnetic spin waves to form," researcher Dima Afanasiev says. “However, to demonstrate that the spin waves can be used for computing, it must be shown that laser-excited spin waves can actually interact”, researcher Alexey Kimel adds.
Controlling properties of spin waves
To achieve this, the researchers used a pair of intense laser pulses with a short but precisely controllable delay between them. The first pulse excites a spin wave, while the second control pulse modifies its properties based on the spin state at the time of its arrival. The researchers demonstrated that this control extends beyond simply adjusting the amplitude and phase; it also involves modifying the frequency and wavelength, thereby enabling magnon conversion. “We believe that this is a real step forward to realize THz spin-wave logic”, Afanasiev concludes.
